A continuing challenge in the semiconductor industry is to find nanoscale transistors that have sufficient performance characteristics for use in today's advanced electrical applications. Bipolar transistors tend to have improved performance characteristics as compared to CMOS transistor configurations.
For example, ultra-high speed bipolar transistors such as SiGe and SiGe:C npn transistors have been demonstrated with gain-bandwidth products as high as 350 GHz. Some bipolar SiGe and SiGe:C pnp transistors demonstrate cutoff frequencies in the range of 25-115 GHz. Unfortunately, bipolar transistors can often be large in size, which can limit their use in nanoscale applications.
On the other hand, achieving comparable performance characteristics with CMOS transistors at the nanoscale level can be costly due to increased processing complexity and/or increased power consumption associated with CMOS transistor fabrication and/or performance. Therefore, it can be beneficial to produce bipolar transistors having a reduced size for use in nanoscale applications.